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We describe a novel quantitative real-time (Q)-PCR assay for Listeria monocytogenes based on the coamplification of a target hly gene fragment and an internal amplification control (IAC). The IAC is a chimeric double-stranded DNA containing a fragment of the rapeseed BnACCg8 gene flanked by the hly-specific target sequences. This IAC is detected using a second TaqMan probe labeled with a different fluorophore, enabling the simultaneous monitoring of the hly and IAC signals. The hly-IAC assay had a specificity and sensitivity of 100%, as assessed using 49 L. monocytogenes isolates of different serotypes and 96 strains of nontarget bacteria, including 51 Listeria isolates. The detection and quantification limits were 8 and 30 genome equivalents, and the coefficients for PCR linearity (R 2 ) and efficiency (E) were 0.997 and 0.80, respectively. We tested the performance of the hly-IAC Q-PCR assay using various broth media and food matrices. Fraser and half-Fraser media, raw pork, and raw or cold-smoked salmon were strongly PCR-inhibitory. This Q-PCR assay for L. monocytogenes, the first incorporating an IAC to be described for quantitative detection of a food-borne pathogen, is a simple and robust tool facilitating the identification of false negatives or underestimations of contamination loads due to PCR failure.

The Gram positive genus Listeria comprises six species, two of which -Listeria monocytogenes and Listeria ivanovii -are pathogenic. Both bacteria are facultative intracellular parasites able to infect macrophages and non-phagocytic cells, such as epithelial cells. After internalization, they undergo a characteristic intracellular infection cycle involving early escape from the phagocytic vacuole, rapid cytosolic replication, actin-based motility, and direct (cell-to-cell) spread to neighbouring cells, where the cycle begins again. Several virulence genes involved in key steps of this cycle are clustered together in a 9 kb locus that is located at the same chromosomal position in L. monocytogenes and L. ivanovii . This central virulence gene cluster or ' Listeria pathogenicity island 1 (LIPI-1)' is absent -or present in a non-functional formin the non-pathogenic Listeria spp. (Vázquez-Boland et al ., 2001a). LIPI-1 encodes a pore-forming toxin (listeriolysin O, LLO) and two phospholipases C (PlcA and PlcB) that cooperate to lyse the phagocytic vacuole membrane; an actin-polymerizing surface protein (ActA), responsible for intracellular bacterial motility and cell-tocell spread; a metalloprotease (Mpl) involved in the maturation of proPlcB; and a transcriptional activator (PrfA) that controls the expression of LIPI-1 genes and of other virulence determinants located elsewhere on the listerial chromosome (Portnoy et al ., 2002;Dussurget et al ., 2004). The latter include hpt , encoding a hexose phosphate transporter (Hpt) required for rapid cytosolic replication (Chico-Calero et al ., 2002), present in both L. monocytogenes and L. ivanovii ; and the inlAB operon, encoding two surface proteins (InlA and InlB) that mediate host cell invasion (Cossart et al ., 2003), only found to date in L. monocytogenes .

The ability to culture neural progenitor cells from the adult human brain has provided an exciting opportunity to develop and test potential therapies on adult human brain cells. To achieve a reliable and reproducible adult human neural progenitor cell (AhNPC) culture system for this purpose, this study fully characterized the cellular composition of the AhNPC cultures, as well as the possible changes to this in vitro system over prolonged culture periods. We isolated cells from the neurogenic subventricular zone/hippocampus (SVZ/HP) of the adult human brain and found a heterogeneous culture population comprised of several types of post-mitotic brain cells (neurons, astrocytes, and microglia), and more importantly, two distinct mitotic cell populations; the AhNPCs, and the fibroblast-like cells (FbCs). These two populations can easily be mistaken for a single population of AhNPCs, as they both proliferate under AhNPC culture conditions, form spheres and express neural progenitor cell and early neuronal markers, all of which are characteristics of AhNPCs in vitro. However, despite these similarities under proliferating conditions, under neuronal differentiation conditions, only the AhNPCs differentiated into functional neurons and glia. Furthermore, AhNPCs showed limited proliferative capacity that resulted in their depletion from culture by 5–6 passages, while the FbCs, which appear to be from a neurovascular origin, displayed a greater proliferative capacity and dominated the long-term cultures. This gradual change in cellular composition resulted in a progressive decline in neurogenic potential without the apparent loss of self-renewal in our cultures. These results demonstrate that while AhNPCs and FbCs behave similarly under proliferative conditions, they are two different cell populations. This information is vital for the interpretation and reproducibility of AhNPC experiments and suggests an ideal time frame for conducting AhNPC-based experiments.

Sphingomyelinases C are enzymes that catalyze the hydrolysis of sphingomyelin in biological membranes to ceramide and phosphorylcholine. Various pathogenic bacteria produce secreted neutral sphingomyelinases C that act as membrane-damaging virulence factors. Mammalian neutral sphingomyelinases C, which display sequence homology to the bacterial enzymes, are involved in sphingolipid metabolism and signaling. This article describes the first structure to be determined for a member of the neutral sphingomyelinase C family, SmcL, from the intracellular bacterial pathogen Listeria ivanovii. The structure has been refined to 1.9-Å resolution with phases derived by single isomorphous replacement with anomalous scattering techniques from a single iridium derivative. SmcL adopts a DNase I-like fold, and is the first member of this protein superfamily to have its structure determined that acts as a phospholipase. The structure reveals several unique features that adapt the protein to its phospholipid substrate. These include large hydrophobic ␤-hairpin and hydrophobic loops surrounding the active site that may bind and penetrate the lipid bilayer to position sphingomyelin in a catalytically competent position. The structure also provides insight into the proposed general base/acid catalytic mechanism, in which His-325 and His-185 play key roles. Sphingomyelinases C (SMases C)4 (EC 3.1.4.12) are phosphodiesterases that catalyze the hydrolysis of the membrane phospholipid sphingomyelin (SM) at the aqueous:lipid interface, generating ceramide and phosphorylcholine. Several types of enzymes with SMase C activity have been identified in eukaryotes and prokaryotes. Eukaryotic SMases C have been classified according to their pH optima and are known as acid SMase (1), alkaline SMase (2), and neutral SMase (nSMase) (3, 4). In prokaryotes, some broad specificity phosphatidylcholine phospholipases C display SM hydrolyzing activity (5, 6) but a number of pathogenic bacteria, such as Staphylococcus aureus (␤-toxin (7)), Bacillus cereus (8), Leptospira interrogans (9), and Listeria ivanovii (10), produce SM-specific phospholipases. These bacterial SMases C share sequence homology with the eukaryotic nSMases, and all currently available data suggests that eukaryotic nSMases and bacterial SMases C (henceforth bacterial nSMases) share a similar catalytic mechanism and overall structure (11,12). A sequence alignment of selected members of the nSMase family is presented in Fig. 1. In contrast to the eukaryotic and bacterial nSMases there is no identifiable sequence conservation within the other types of SMase C. Additionally, these enzymes utilize different catalytic mechanisms, and are predicted to be structurally unrelated to nSMases.Mammalian nSMases are thought to play a key role in sphingolipid metabolism and there is increasing evidence implicating SM metabolites in cell signaling, cell proliferation, and apoptosis (13-16). Two human nSMases have been cloned, nSMase1 (3) and nSMase2 (4). Sequence analysis of these proteins and other e...

The human brain is a highly vascular organ in which the blood-brain barrier (BBB) tightly regulates molecules entering the brain. Pericytes are an integral cell type of the BBB, regulating vascular integrity, neuroinflammation, angiogenesis and wound repair. Despite their importance, identifying pericytes amongst other perivascular cell types and deciphering their specific role in the neurovasculature remains a challenge. Using primary adult human brain cultures and fluorescent-activated cell sorting, we identified two CD73+CD45− mesenchymal populations that showed either high or low CD90 expression. CD90 is known to be present on neurons in the brain and peripheral blood vessels. We found in the human brain, that CD90 immunostaining localised to the neurovasculature and often associated with pericytes. In vitro, CD90+ cells exhibited higher basal proliferation, lower expression of markers αSMA and CD140b, produced less extracellular matrix (ECM) proteins, and exhibited lesser pro-inflammatory responses when compared to the CD90− population. Thus, CD90 distinguishes two interrelated, yet functionally distinct pericyte populations in the adult human brain that may have discrete roles in neurovascular function, immune response and scar formation.

Cellular interactions mediated by the neural cell adhesion molecule (NCAM) are critical in cell migration, differentiation and plasticity. Switching of the NCAM-interaction mode, from adhesion to signalling, is determined by NCAM carrying a particular post-translational modification, polysialic acid (PSA). Regulation of cell-surface PSA-NCAM is traditionally viewed as a direct consequence of polysialyltransferase activity. Taking advantage of the polysialyltransferase Ca 2+ -dependent activity, we demonstrate in TE671 cells that downregulation of PSA-NCAM synthesis constitutes a necessary but not sufficient condition to reduce cell-surface PSA-NCAM; instead, PSA-NCAM turnover required internalization of the molecule into the cytosol. PSA-NCAM internalization was specifically triggered by collagen in the extracellular matrix (ECM) and prevented by insulin-like growth factor (IGF1) and insulin. Our results pose a novel role for IGF1 and insulin in controlling cell migration through modulation of PSA-NCAM turnover at the cell surface.

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